Aircraft wing with a moveable wing tip device for load alleviation

Abstract

An aircraft is disclosed having a wing, the wing having a fixed wing with a wing tip device moveably mounted about a hinge at the tip thereof. The wing tip device is operable between a flight configuration, and a load alleviating configuration for load alleviation during flight. The aircraft includes a restraining assembly operable between a restraining mode in which the wing tip device is held in the flight configuration using a restraining force such as by a brake, and a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device may adopt the load alleviating configuration.

The invention claimed is: 
     
       1. An aircraft comprising a wing, the wing having a fixed wing with a wing tip device moveably mounted at the tip thereof, wherein the fixed wing has an upper surface and a lower surface, and the wing tip device has an upper surface and a lower surface, and the wing tip device is operable between:
 (i) a flight configuration for use during flight, in which configuration the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing; and 
 (ii) a load alleviating configuration for load alleviation during flight, in which configuration the wing tip device is moved relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is moved away from the respective surface of the fixed wing, and the load on the wing is reduced; wherein the aircraft comprises 
 an actuator arranged to move the wing tip device between the flight configuration and the ground configuration, and 
 a restraining assembly operable between
 a restraining mode in which the wing tip device is held in the flight configuration using a restraining force, and 
 a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device is able to adopt the load alleviating configuration. 
 
 
     
     
       2. An aircraft according to  claim 1 , wherein the wing comprises a biasing member, arranged such that when the wing tip device is in the flight configuration, the biasing member exerts a biasing force to urge the wing tip device towards the load alleviating configuration. 
     
     
       3. An aircraft according to  claim 2 , wherein when the restraining assembly is in the restraining mode, the biasing force is overcome by the restraining force, but when the restraining assembly is in the releasing mode, the biasing force is sufficient to assist in moving the wing tip device into the load alleviating configuration. 
     
     
       4. An aircraft according to  claim 3 , wherein the biasing member is able to be selectively disengaged from exerting the biasing force on the wing tip device. 
     
     
       5. An aircraft according to  claim 4 , wherein the wing comprises a clutch for selectively disengaging the biasing member from exerting the biasing force on the wing tip device. 
     
     
       6. An aircraft according to  claim 1 , further comprising a control system arranged to control operation of the restraining assembly between the restraining and the releasing modes. 
     
     
       7. An aircraft according to  claim 6 , wherein the aircraft comprises an alpha detector for detecting the angle of attack of the aircraft relative to the freestream flow, and wherein the control system is configured to switch operation of the restraining assembly from the restraining mode to the releasing mode in response to the detected angle of attack exceeding a predetermined threshold. 
     
     
       8. An aircraft according to  claim 7 , wherein the alpha detector is located on the aircraft nose such that it is located upstream of the wing tip device. 
     
     
       9. An aircraft according to  claim 6 , wherein the control system is configured to switch operation of the restraining assembly from the restraining mode to the releasing mode in response to an input indicative of the aircraft being in the landing and/or take-off phases. 
     
     
       10. An aircraft according to  claim 6 , wherein the aircraft comprises a corresponding fixed wing, wing tip device and restraining assembly, on the other side of the aircraft fuselage, and wherein the control system is configured to switch operation of one of the restraining assemblies from the restraining mode to the releasing mode in response to an input indicative of the other of the restraining assembles having already switched to the releasing mode. 
     
     
       11. An aircraft according to  claim 1 , wherein the wing tip device is also operable to
 (iii) a ground configuration for use during ground-based operations, in which ground configuration the wing tip device is moved away from the flight configuration such that the span of the aircraft wing is reduced. 
 
     
     
       12. An aircraft according to  claim 1 , wherein the actuator is also arranged to move the wing tip device from the load alleviating configuration back to the flight configuration. 
     
     
       13. An aircraft according to  claim 1 , wherein when the restraining assembly is in the restraining mode, the actuator is in a passive state such that it does not actively contribute to the restraining force. 
     
     
       14. An aircraft according to  claim 1 , wherein the wing tip device is rotatably mounted on a hinge at the tip of the wing, such that it may rotate, about the hinge, between the flight and load alleviating configurations. 
     
     
       15. An aircraft according to  claim 14 , wherein the hinge is orientated non-parallel to the line-of flight direction. 
     
     
       16. An aircraft according to  claim 15 , wherein the hinge is orientated substantially perpendicular to the swept mean chord axis of the wing. 
     
     
       17. An aircraft according to  claim 14 , wherein the hinge is a double hinge for allowing upwards and downwards rotation of the wing tip device. 
     
     
       18. A restraining assembly configured to be installed on an aircraft wing for the aircraft according to  claim 1 , and being operable between a restraining mode in which a wing tip device is held in the flight configuration using a restraining force, and a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device is able to adopt a load alleviating configuration. 
     
     
       19. An aircraft wing, comprising:
 a fixed wing with a wing tip device moveably mounted at the tip thereof, wherein the fixed wing has an upper surface and a lower surface, and the wing tip device has an upper surface and a lower surface, and the wing tip device is operable between: 
 (i) a flight configuration for use during flight, in which configuration the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing; and 
 (ii) a load alleviating configuration for load alleviation during flight, in which configuration the wing tip device is moved relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is moved away from the respective surface of the fixed wing, and the load on the wing is reduced; 
 wherein the wing comprises
 an actuator arranged to move the wing tip device between the flight configuration and the ground configuration, and 
 a restraining assembly operable between
 a restraining mode in which the wing tip device is held in the flight configuration using a restraining force, and 
 a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device may adopt the load alleviating configuration. 
 
 
 
     
     
       20. A method of controlling load alleviation on a wing having a fixed wing with a wing tip device moveably mounted at the tip thereof, wherein wing has an upper surface and a lower surface, and the wing tip device has an upper surface and a lower surface, and an actuator arranged to move the wing tip device between the flight configuration and the ground configuration, the method comprising the steps of:
 (a) holding the wing tip device in a flight configuration using a restraining force, in which flight configuration the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing; and 
 (b) releasing the restraining force to allow the wing tip device to adopt a load alleviating configuration for load alleviation during flight, in which configuration the wing tip device is moved relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is move away from the respective surface of the fixed wing, and the load on the wing is reduced. 
 
     
     
       21. An aircraft comprising a wing, the wing having a fixed wing with a wing tip device moveably mounted at the tip thereof, wherein the fixed wing has an upper surface and a lower surface, and the wing tip device has an upper surface and a lower surface, and the wing tip device is operable between:
 (i) a flight configuration for use during flight, in which configuration the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing; and 
 (ii) a load alleviating configuration for load alleviation during flight, in which configuration the wing tip device is moved relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is moved away from the respective surface of the fixed wing, and the load on the wing is reduced; wherein the aircraft comprises 
 a restraining assembly operable between
 a restraining mode in which the wing tip device is held in the flight configuration using a restraining force, 
 a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device is able to adopt the load alleviating configuration, and 
 
 wherein the wing tip device is entirely free to rotate when the restraining assembly is in the releasing mode.